Disk cartridge

ABSTRACT

A disk cartridge which comprises a cartridge case, a disk rotatably encased in the cartridge case, and a cleaning sheet supported on the inside surface of the cartridge case by welding, the cartridge case being composed of a thermoplastic synthetic resin, and the cleaning sheet being composed at least of a mixed fabric of acrylic fibers and rayon fibers and being fixed to the inside surfaces of the cartridge case by welding has distinguished disk-handling characteristics and cartridge case-fixing characteristics.

BACKGROUND OF THE INVENTION

A disk cartridge, for example, a magnetic disk cartridge, mainlycomprises a cartridge case having openings for inserting magnetic headsand openings for inserting a rotation driving shaft, a flexible magneticdisk rotatably encased in the cartridge case, and a cleaning sheetsupported on the inside surfaces of the cartridge case.

The cleaning sheet for the conventional magnetic disk cartridge iscomposed of a non-woven fabric made of, for example, mixed-fibers ofrayon and polypropylene, mixed fibers of rayon and polyethyleneterephthalate, or single fibers of polyethylene terephthalate, and isfixed to the inside surfaces of a cartridge case by ultrasonic welding,heat seal, or by an adhesive.

However, the cleaning sheets composed of the fibers do not perform goodcleanability of the magnetic disk, and further have such problems as thedevelopment of scratches on the magnetic disk surface by sliding contactwith the cleaning sheet, falling-away of the fibers from the cleaningsheet by sliding contact with the magnetic disk, and attachment of thefalling-away fibers to the magnetic disk or the magnetic head, therebyadversely affecting the recording-reproducing characteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a disk cartridge, suchas a magnetic disk cartridge, which has markedly improved disk-handlingcharacteristics and cartridge case-fixing characteristics, and a highwelding strength of the cleaning sheets to the cartridge case.

The present invention is directed to a disk cartridge which comprises acartridge case composed of a flexible sheet or a molding of rigidsynthetic resin, a flexible disk rotatably encased in the cartridgecase, and a cleaning sheet supported on the inside surface of thecartridge case by welding.

According to a first aspect of the present invention, the cartridge caseis composed of a thermoplastic synthetic resin and the cleaning sheet iscomposed at least of a mixed fabric comprising acrylic fibers and rayonfibers.

According to a second aspect of the present invention, the cleaningsheet is composed of a sheet member of multi-layer structure comprisinga disk-facing non-woven fabric layer composed of a non-woven fabric mademainly of acrylic fibers on the disk-facing side, a cartridgecase-facing non-woven fabric layer composed of a non-woven fabriccontaining fibers at least a portion of which are embeddable into theinside surface of the cartridge case by welding of the cleaning sheet tothe cartridge case while substantially retaining the fiber form, and anintermediate layer being provided between the disk-facing non-wovenfabric layer and the cartridge-facing non-woven fabric layer and beingcomposed of a mixed fabric comprising acrylic fibers and rayon fibers.

As described above, the desired disk-handling characteristics of thecleaning sheet are specifically am ability to clean a disk such as amagnetic disk, an ability to avoid scratching the disk, and a low lintcharacteristic of the cleaning sheet when in sliding contact with thedisk. We have made extensive studies of non-woven fabrics for thecleaning sheet and have found that non-woven fabrics made of acrylicfibers alone have markedly improved disk-handling characteristics.

However, the non-woven fabrics composed of the acrylic fibers alonestill have some problems. That is, when the non-woven fabrics composedof the acrylic fibers alone are subjected to heat sealing to the insidesurfaces of a cartridge case, the acrylic fibers are liable to burn outwhile the fibers undergo shrinking and fusion owing to thecharacteristics of the acrylic fibers. Consequently, the cleaning sheetcannot have a satisfactory welding strength to the cartridge case, andthe cleaning sheet may be peeled off from the cartridge case byrepetitious of sliding contact with the disk, or hard materials may beformed on the surface of the cleaning sheet, lowering the cleanliness ofthe disk, of impart more severe scratches to the disk. Thus, thedesirable characteristics of the acrylic fibers are lost.

In the present invention, all the foregoing problems have been solved bymaking the cleaning sheet from a mixed fabric of acrylic fibers andrayon fibers.

The thermoplastic synthetic resin for the cartridge case includes, forexample, polyvinyl chloride, ABS resin, polyacetal resin, polystyreneresin, etc. and a desired cartridge case can be formed therefrom in ajacket shape or by injection molding.

The magnetic disk is prepared by forming a thin magnetic film on oneside or both sides of a base film made of polyester, polyimide, or thelike by an appropriate means such as coating, vapor deposition, orsputtering, so as to have an appropriate flexibility.

The structure of a cleaning sheet fixed to and supported on the insidesurface of a cartridge case will be described in detail below, referringto embodiments by way of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 show a magnetic disk cartridge according to a firstembodiment of the present invention, where FIG. 1 is a bottom plan viewof the magnetic disk cartridge;

FIG. 2 is an unfolded view of the cartridge case and the cleaning sheetof the magnetic disk cartridge;

FIG. 3 is a plan view of the cleaning sheet before being fixed to thecartridge case;

FIG. 4 is a dismantled, schematic view of a magnetic disk cartridgeaccording to a second embodiment of the present invention;

FIG. 5 is a bottom plan view of an upper case of the magnetic diskcartridge of FIG. 4 where the cleaning sheet is provided thereon;

FIG. 6 is a plan view of a lower case of the magnetic disk cartridge ofFIG. 4 where the cleaning sheet is provided thereon;

FIG. 7 is an enlarged, cross-sectional view of the neighborhood of theopenings for inserting the magnetic heads while the magnetic diskcartridge of FIG. 4 is put into operation;

FIG. 8 is an enlarged, cross-sectional view of the neighborhood of theelastic piece of the magnetic disk cartridge of FIG. 4;

FIG. 9 is an enlarged cross-sectional view of the cleaning sheetaccording to third embodiment of the present invention;

FIG. 10 is a schematic view of a process for preparing the cleaningsheet;

FIG. 11 is a partially enlarged, cross-sectional view of a linking statebetween the cartridge case and the fiber of the cleaning sheet;

FIG. 12 is an enlarged cross-sectional view of a cleaning sheetaccording to a fourth embodiment of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

In FIGS. 1 to 3, a disk cartridge comprises a cartridge case 1, aflexible, sheet-formed magnetic disk 2 rotatably encased in thecartridge case 1, and a cleaning sheet 3 fixed to the inside surface ofthe cartridge case 1. As shown in FIG. 2, the cartridge case 1 iscomposed of a rectangular case sheet member 4 made of, for example,polyvinyl chloride, and three extended edge parts 5a, 5b and 5c forwelding are provided at a half section 4b of the case sheet member 4. Arectangular cleaning sheet member 6 having substantially the same areaas that of the rectangular case sheet member 4 is fixed to one side ofthe case sheet member 4 by welding, as will be described later.

In the two square sections 4a and 4b, and 6a and 6b of the case sheetmember 4 and the cleaning sheet member 6, respectively, divided by acenter folding line X (imaginary line), openings 8 for inserting arotation driving shaft, which are larger in diameter than the centerhole 7 of the magnetic disk 2 (see FIG. 1) and are directed to exposethe peripheral part around the center hole 7, openings 9 for insertingmagnetic heads, detection openings 10 for detecting the index hole ofthe magnetic disk 2, thereby correctly tracking the magnetic disk 2,notches 11 for detecting the side A or B of the magnetic disk cartridge,etc. are provided at symmetrical positions along the center folding lineX.

After the cleaning sheet member 6 has been placed on the case sheetmember 4, the cleaning sheet member 6 is subjected to spotwise welding12 substantially all over the cleaning sheet member 6, whereas theperipheral parts around the openings 8 for inserting a rotation drivingshaft, the openings 9 for inserting magnetic heads, the detectionopenings 10 and the notches 11 are subjected to linear welding 13, asshown in FIG. 2, whereby the cleaning sheet members 6 can be fixed tothe case sheet member 4 without impairing the softness and elasticity ofthe cleaning sheet member 6. In this case, it is not always necessary tomake the spotwise welding 12 all over the cleaning sheet member 6, butto such a degree that the cleaning sheet member 6 is so fixed as not tobe readily released from the case sheet member 4.

Then, the case sheet member 4 is folded along the center folding line Xso that the cleaning sheet member 6 may be on the inside, and theextended edge parts 5a and 5c, which are counterposed to each other,among the three extended edge parts 5a, 5b and 5c for welding providedon the square section 4b, are folded over the outside of the othersquare section 4a, and subjected to partial welding 14 to prepare anenvelope having an open end. A magnetic disk 2 stamped out of a magneticsheet is inserted into the envelope, and then the remaining extendededge part 5b for welding is folded over the outside of the squaresection 4a and subjected to spotwise welding 14, whereby the magneticdisk cartridge as shown in FIG. 1 can be built up.

According to the first aspect of the present invention, the cleaningsheet 3 is composed of a mixed fabric of acrylic fibers and rayon fibersor a mixed fabric of acrylic fibers, rayon fibers and heat-meltablefibers.

The acrylic fibers are synthetic fibers containing more than about 85%of acrylonitrile, copolymerized with acrylate ester, vinyl acetate,styrenesulfonic acid, etc. to improve the frictional resistance or wearresistance, look like wool most among the synthetic fibers and have adistinguished soft-tough flexibility. The acrylic fibers (staples) havea tensile strength of about 2.5 to about 5.0 g/D, an elongation of about25 to about 50%, an elastic elongation of about 90 to about 95% (at 3%elongation) and a specific gravity of about 1.14 to about 1.17. In thepresent invention, acrylic fibers having sizes of about 1 to about 6denier are preferably used.

The rayon fibers for use in the present invention includes, for example,viscose rayon fibers, cuproammonium rayon fibers, acetate rayon fibers,etc. The rayon fibers (staples) have a tensile strength of about 2.5 toabout 3.1 g/D, an elongation of about 16 to about 22%, an elasticelongation of about 55 to about 80% (at 3% elongation) and a specificgravity of about 1.50 to about 1.52.

The heat-meltable fibers for use in the present invention include, forexample, polyethylene terephthalate fibers, polypropylene fibers,polyvinyl chloride fibers, vinyl chloride-vinyl acetate copolymerfibers, polyamide fibers, etc.

In case of a mixed fabric of acrylic fibers and rayon fibers, it ispreferable that the mixed fabric is composed of 80 to 20% by weight ofacrylic fibers and 20 to 80% by weight of rayon fibers. In case of morethan 80% by weight of acrylic fibers, the welding strength of thecleaning sheet to the cartridge case is lowered, and hard materials areformed on the surface of the cleaning sheet, giving scratches to thedisk, whereas in case of less than 20% by weight of acrylic fibers, muchfalling away of fibers takes place, lowering the cleanability,cuttability, etc.

When the cleaning sheet is composed of a mixed fabric of acrylic fibers,rayon fibers and heat-meltable fibers, it is preferable that the mixedfabric is composed of 80 to 20% by weight of acrylic fibers, 20 to 80%by weight of rayon fibers and 5 to 30% by weight of heat-meltablefibers, total being 100% by weight. In case of more than 80% by weightof the acrylic fibers, the welding strength is lowered, and hardmaterials are formed during the welding, whereas in case of less than20% by weight of the acrylic fibers, the cleanability, cuttability, etc.are lowered. The heat-meltable fibers are added to the fabric to improvethe adhesion between the fibers, and in case of more than 30% by weightof the heat-meltable fibers, the cleanability, cuttability, etc. arelowered.

Polyvinyl chloride sheet that makes the cartridge case 1 (case sheetmember 4) softens at about 65° to about 85° C. and is plasticized atabout 120° to about 150° C. and starts to melt at about 170° C., whilethe rayon fibers in the cleaning sheet 3 (cleaning sheet member 6) has aproperty to decompose at about 260° to about 300° C. by heating withoutsoftening or melting. Thus, when the cleaning sheet 3 (cleaning sheetmember 6) is subjected to welding to the cartridge case 1 (case sheetmember 4) under some pressure, the rayon fibers 24 in the cleaning sheet3 (cleaning sheet member 6) are embedded into the inside surface layerof the cartridge case 1 (case sheet member 4), while retaining the fiberform as shown in FIG. 11. Since the cross-sectional shapes of the rayonfibers 24 are non-circular, the cleaning sheet 3 can be firmly fixed toand held in the cartridge case 1, when the rayon fibers are embeddedinto the cartridge case 1 (case sheet member 4).

The remaining parts of the embedded rayon fibers 24 are in an entangledstate with one another and with other fibers in the fabric, andultimately the cleaning sheet 3 can be firmly fixed to and held in thecartridge case 1 thereby.

The heat-meltable fibers in the cleaning sheet 3 serve to reinforce thebinding of acrylic fibers and rayon fibers, and the binding of cartridgecase 1 and cleaning sheet 3.

The cleaning sheet member 6 is passed between rollers each providedwith, for example, a knurling tool around the roller surface (embossingtreatment), whereby an embossing pattern 23 can be formed on thecleaning sheet member 6, as shown in FIG. 3. In FIG. 2, the embossingpattern 23 are not shown for simplifying the drawing. Then, the thusembossed cleaning sheet member 6 is fixed to the case sheet member 4 byspotwise welding 12 and also by linear welding 13, as already describedbefore.

Magnetic disk cartridges were prepared, using cartridge cases preparedin the following manner:

A cartridge case to which a cleaning sheet composed of mixed fabric of50% by weight of acrylic fibers and 50% by weight of rayon fibers wasfixed by heat sealing (Example 1); a cartridge case to which a cleaningsheet composed of a fabric of 60% by weight of acrylic fibers, 30% byweight of rayon fibers and 10% by weight of polyethylene terephthalatefibers was fixed by heat sealing (Example 2); a cartridge case to whicha cleaning sheet composed of non-woven fabric of acrylic fibers alonewas fixed by heat sealing (Comparative Example); a cartridge case towhich a cleaning sheet composed of non-woven fabric of 80% by weight ofrayon fibers and 20% by weight of polypropylene fibers was fixed by heatsealing (Comparative Example 1); and a cartridge case to which acleaning sheet composed of non-woven fabric of polyethyleneterephthalate fibers above was fixed by heat sealing (ComparativeExample 2).

Cuttability, cleanability, magnetic disk scratchability, lintcharacteristics and weldability of the cleaning sheets of Example 1,Example 2, Comparative Example, and Conventional Examples 1 and 2 weredetermined according to the following procedures.

A. Cuttability

The respective cleaning sheet members 6 were fixed to the case sheetmembers 4 and then subjected to punching at a punching speed of 120punchings per minute to provide openings 8 for inserting a rotationdriving shaft and openings 9 for inserting magnetic heads together withthe case sheet members 4. State of fluffy occurrence at cut parts of theopenings 8 and 9 was observed.

B. Cleanability

The respective magnetic disk cartridges were placed in a recordingreproducing apparatus, and the magnetic disk 2 was made to turn in thecartridge case 1, and a small amount of iron powders was added into thecartridge case 1 from the openings 9 for inserting the magnetic heads.Then, the disk was made to turn for 10 minutes. Then, the cartridge case1 was unfolded to observe the state of adhesion of the iron powders tothe cleaning sheet 3.

C. Magnetic disk scratchability

By turning a magnetic disk in the respective magnetic cartridge casecontinuously for one week (168 hours) at the ordinary temperature,occurrence of scratches on the magnetic disk by the respective cleaningsheets was observed.

D. Lint characteristics

A predetermined amount of the respective cleaning sheets were dipped ina Freon solvent and subjected to ultrasonic vibrations for 10 minutes toobserve the state of falling away of the fibers from the respectivecleaning sheets.

E. Weldability

The respective cleaning sheet members 6 were spotwise welded to the casesheet members 4 at a spot distance of 7 mm by welding to once fix thecleaning sheet members 6 to the case sheet members 4. An edge part ofthe welded cleaning sheet members 6 were peeled off from the case sheetmembers 4 to a length of about 5 cm at a width of about 1 cm in a stripeform, while leaving the remaining body part as fixed on the case sheetmember 4. By placing the case sheet member 4 on the upside and thecleaning sheet member 6 on the downside, the peeled part of the cleaningsheet member 6 was made to hang down from the case sheet member 4. Aload was applied in the peeling direction of the cleaning sheet member 6from the case sheet member 4 by fixing a weight to the tip end of thehanging-down part of the cleaning sheet member 6. A load weight (g) withwhich the fixed part (welded part) of the cleaning sheet member 6started to peel off from the case sheet member 4 was measured by slowlyincreasing the weight.

The results of these tests are shown in the following Table 1.

                                      TABLE 1                                     __________________________________________________________________________                            Scratch-                                                                             Lint                                           Sample Cuttability                                                                           Cleanability                                                                           ability                                                                              Characteristics                                                                       Weldability                            __________________________________________________________________________           No substantial                                                                        Much attachment Slight falling                                 Example 1                                                                            fluffy  of iron  No scratches                                                                         away of fibers                                                                        100                                                                              g                                          development                                                                           powders  observed                                                                             observed                                              No substantial                                                                        Much attachment No substantial                                 Example 2                                                                            fluffy  of iron  No scratches                                                                         falling away                                                                          100                                                                              g                                          development                                                                           powders         of fibers                                             No substantial                                                                        Much attachment No substantial                                 Comparative                                                                          fluffy  of iron  No scratches                                                                         falling away                                                                          10 g                                   Example                                                                              development                                                                           powders  observed                                                                             of fibers                                             No substantial                                                                        Rather less                                                                            Considerable                                                                         A few falling                                  Conventional                                                                         fluffy  attachment of                                                                          scratches                                                                            away of fibers                                                                        100                                                                              g                                   Example 1                                                                            development                                                                           iron powders                                                                           observed                                                                             observed                                              Many fluffy                                                                           Less attachment Slight falling                                 Conventional                                                                         developments                                                                          of iron  Scratches                                                                            away of fibers                                                                        20 g                                   Example 2                                                                            observed                                                                              powders  observable                                                                           observed                                       __________________________________________________________________________

As is obvious from the foregoing test results, the present magnetic diskcartridges according to Examples 1 and 2 have better cuttability,cleanability, magnetic disk scratchability, lint characteristics andweldability than those according to Comparative Example and ConventionalExamples 1 and 2.

In FIGS. 4 to 8, a second embodiment of the present invention is shown.

As shown in FIG. 4, a magnetic disk cartridge comprises a cartridge case26, a magnetic disk 27 rotatably encased in the cartridge case 26, and ashutter 28 slidably supported on the cartridge case 26.

The cartridge case 26 is composed of an upper case 26a and a lower case26b, which are injection molded from a rigid resin, for example, ABSresin.

An opening 29 for inserting a rotation driving shaft is providedsubstantially at the center of the lower case 26b, and a rectangularopening 30 for inserting a magnetic head is provided near the opening29. Similarly, an opening for inserting the magnetic head is provided onthe upper case 26a. At the parts near the front side of the upper andlower cases 26a and 26b, there are provided recesses 31 in a slightdepth to control the sliding range of the shutter 28. The said openings30 for inserting the magnetic heads are provided at the intermediateposition in the recesses 31.

As shown in FIG. 5, recesses 42 and 42 are provided on the insidesurface of the upper case 26a and on both sides along the opening 30 forinserting the magnetic head. The longitudinal width W1 of the recesses42 is controlled to be substantially equal to the width (longitudinalwidth) W2 in the longitudinal direction of the opening 30 for insertingthe magnetic head, and the lateral width W3 of the recesses 42 iscontrolled to be at least 0.3 times, preferably 0.5 to 1.5 times thewidth (lateral width) W4 in the direction perpendicular to thelongitudinal direction of the opening 30 for inserting the magnetichead. On the disk-coming side in the disk-turning direction with respectto the opening 30 for inserting the magnetic head on the upper case 26athere are provided projections 43 extended in a large number of rows,where the projections in both outermost rows are slightly higher thanthe rows 43 in the inner rows.

On the inside surface of the upper case 26a, there are providedarc-formed control ribs 44 that control the encasing position of themagnetic disk 27, and a part of the control rib 44 extends over the edgepart of the recess 42 to serve as a reinforcing member for theperipheral edge of the recess 42.

As shown in FIG. 5, a substantially C-shaped cleaning sheet 45 havingthe same structure as that of the said first embodiment is placed withinthe control ribs 44. Lateral width W5 of an opening 46 of the cleaningsheet 45 provided at a position corresponding to the opening 30 forinserting the magnetic head is designed to be slightly larger than thelateral width W4 of the opening 30 for inserting the magnetic head. Byplacing the cleaning sheet 45 on the inside surface of the upper case26a, the recess 42 and the projections 43 are covered by the cleaningsheet 45 and the cleaning sheet 45 is welded to the upper case 26a onthe peripheral part by ultrasonic welding or heat sealing. Since therecess 42 of the upper case 26a has a sufficient area, as describedabove, the edge part of the opening 46 of the cleaning sheet 45 can bewelded within the recess 42 as shown by 47 in FIG. 7.

As shown in FIG. 6, a support 48 for elastically supporting an elasticpiece 50 and the projected rows 49 for preventing the magnetic sheetfrom protruding are provided on the inside surface of the lower case 26bat positions substantially counterposed to the projections 43 on theupper case 26a. As shown in FIG. 6 and FIG. 8, the base part 51 of anelastic piece 50 formed by folding a plastic sheet is fixed to theposition near the support 48 on the inside surface of the lower case 26bby an appropriate means by bonding or heat sealing. The free end 52 ofthe elastic piece 50 is supported by the support 48 and retained in aninclined state.

Also on the inside surface of the lower case 26b, there are projectedcontrol ribs 44. The cleaning sheet 45 is placed within the control ribs44. Lateral width W5 of the opening 46 of the cleaning sheet 45 providedat the position corresponding to the opening 30 for inserting themagnetic head is designed to be somewhat larger than the lateral widthW4 of the opening 30 for inserting the magnetic head. As shown in FIG.6, the elastic piece 50 is covered by the cleaning sheet 45 within thecontrol ribs 44 on the lower case 26b, and the cleaning sheet 45 iswelded to the lower case 26b at the peripheral part as shown by spots47, but the welding is not carried out in the area near the elasticpiece 50.

When a magnetic disk cartridge is built up with the upper case 26a andthe lower case 26b, the cleaning sheet 45 on the lower case 26b ispartially lifted by the elastic piece 50, as shown in FIG. 8, and alsothe lifting is somewhat lowered by the projections 43 provided on theupper case 26a to elastically pinch the magnetic disk 27 by the upperand lower cleaning sheets 45. The disk surfaces are cleaned by thecleaning sheets 45 as the magnetic disk 27 turns.

FIG. 7 shows the state of the disk cartridge in operation where numeral53 is magnetic heads.

In this embodiment, it was found that the magnetic disk cartridge hadbetter cuttability, cleanability, magnetic disk scratchability, lintcharacteristics and weldability than those of cleaning sheet memberscomposed of other materials, as in the case of using the said case sheetmember made of rigid polyvinyl chloride resin.

According to the first aspect of the present invention, the presentcleaning sheet contains acrylic fibers, as described above, which arevery soft and flexible among the synthetic fibers, and have a goodeffect without scratching the turning disk surface and without anyfluffy occurrence. Owing to the good cuttability, a portion of fibersnever protrude, for example, from the edges of the openings forinserting the magnetic head or a rotation driving shaft into theopenings, where a disc cartridge is prepared by cutting. Particularly,when the fibers protrude into the openings for inserting the magneticheads, errors may appear during the recording or reproducing owing tothe protruded fibers, but in the present invention no such errors owingto the protruded fibers appear because of the improved cuttability ofacrylic fibers are described above.

Furthermore, the rayon fibers in the cleaning sheet are strongly linkedto the inside surface of a cartridge case, and thus the welding strengthof the cleaning sheet is so high that there is no fear of release of thecleaning sheet from the cartridge case.

Thus, the present invention can provide a magnetic disk cartridge havinga cleaning sheet of distinguished disk-handling characteristics andcartridge case-fixing characteristics.

According to the second aspect of the present invention, a cleaningsheet has the following structure as a third embodiment.

The cleaning sheet 3 is composed of three layers as shown in FIG. 9. Thestructure, etc. of the cleaning sheet 3 will be described in detailbelow, referring to FIGS. 9 to 12.

As shown in FIG. 9, the cleaning sheet 3 comprises a disk-facingnon-woven fabric layer 15, which faces the magnetic disk 2, a cartridgecase-facing non-woven fabric layer 16, which faces the cartridge case 1,and an intermediate layer 17 which links to disk-facing non-woven fabriclayer fabric 15 and the cartridge case-facing non-woven fabric layer 16.

The disk-facing non-woven fabric layer 15 is made of acrylic fibersalone. The acrylic fibers having the properties and characteristics asdescribed before can be also used in the second aspect of the presentinvention.

In the third embodiment, the disk-facing non-woven fabric layer 15 ismade of acrylic fibers alone in order to fully exhibit the improveddisk-handling characteristics of the acrylic fibers. However, thepresent invention is not limited thereto. For example, the acrylicfibers can contain not more than 50% by weight of other kind of fiberssuch as polyethylene terephthalate, polypropylene, polyamide, rayon,etc. in order to enhance the linking strength with the lower layer orimprove the frictional resistance of the layer surface.

The cartridge case-facing non-woven fabric layer 16 is composed of amixed fiber layer of rayon fibers and polyethylene terephthalate fibers,where the mixing ratio of the rayon fibers to the polyethyleneterephthalate fibers by weight can be appropriately selected from arange of about 1/9 to about 9/1, preferably 3/7 to 7/3. The same rayonfibers as already described can be also used in the second aspect of theinvention.

On the other hand, the polyethylene terephthalate fibers are polyesterfibers obtained by polycondensation of terephthalic acid with ethyleneglycol. The polyethylene terephthalate fibers (staples) have a tensilestrength of about 4.7 to about 6.5, an elongation of about 20 to about50%, and elastic elongation of about 90 to about 99% (at 3% elongation)and a specific gravity of about 1.38.

In the second aspect of the present invention, the disk-facing non-wovenfabric layer 15 and the cartridge case-facing non-woven fabric 16 can bebonded together without impairing the distinguished softness of theacrylic fibers in the disk-facing non-woven fabric layer 15 by providingthe intermediate layer 17 composed of a mixed fabric of acrylic fibersand rayon fibers therebetween, since the acrylic fibers are used in thedisk-facing non-woven fabric layer 15 and the rayon fibers are used inthe cartridge case-facing non-woven fabric layer 16, when the matchingof the layer 15 to the layer 16 is taken into account. The mixing ratioof the acrylic fibers to the rayon fibers by weight can be appropriatelyselected from a range of 1/9 to 9/1, preferably 3/7 to 7/3.

Unit area weight of the cleaning sheet 3 composed of such layers asdescribed above may be preferably limited, and is appropriately about 20to about 40 g/m². The unit area weight is an average of 5 samples, 50cm×50 cm, obtained by measuring each weight.

In FIG. 10, one example of preparing the cleaning sheet 3 is shown,where a roll wound with a mixed fiber fabric 18, a roll wound with amixed fiber fabric 19, a roll wound with a single fiber fabric 20 and aroll wound with a single fiber fabric 21 are arranged in this order.

The mixed fiber fabric 18 is a non-woven fabric made of rayon fibers andpolyethylene terephthalate fibers at a mixing ratio of the rayon fibersto the polyethylene terephthalate fibers of 3:7 by weight and ultimatelymade into the cartridge case-facing non-woven fabric layer 16. The mixedfiber fabric 19 is a fabric made of rayon fibers and acrylic fibers at amixing ratio of the rayon fibers to the acrylic fibers of 5:5 by weightand is ultimately made into the intermediate layer 17. The single fiberfabrics 20 and 21 are both non-woven fabrics made of acrylic fibersalone and are ultimately made in the disk-facing non-woven fabric layers15a and 15b, respectively (see FIG. 9).

In FIG. 10, numeral 22 shows individual guide rollers for continuouslyletting out the fabrics 18, 19, 20 and 21, and 23 shows a wiremesh forconveying the overlaid non-woven fabrics. The fabrics 18, 19, 20 and 21each have a thickness of 50 μm, and the fabrics 18, 19, 20 and 21successively laid one upon another on the wiremesh 23 are passed betweenheating rollers, whereby they are controlled to a predeterminedthickness and the fibers mixed in the cartridge case-facing non-wovenfabric layer 16 and the intermediate layer 17 are highly entangled withother fibers while shrunken by the heating. The disk-facing non-wovenfabric layer 15, the cartridge case-facing non-woven fabric layer 16 andthe intermediate layer 17 are integrally linked to one another therebyto form the cleaning sheet member 6.

In this embodiment, a first disk-facing non-woven fabric layer 15b iscomposed of the single fiber fabric 20 and a second disk-facingnon-woven fabric layer 15a is composed of the single fiber fabrics 21,as shown in FIGS. 9 and 10. If the disk-facing non-woven fabric layer 15is composed of a plurality of thin layers, as described above, therewill be such an advantage that the unevenness in the total thickness canbe reduced.

The thus obtained cleaning sheet member 6 is passed between rollers eachprovided with, for example, a knurling tool around the roller surface(embossing treatment), whereby an embossing pattern 23 can be formed onthe cleaning sheet member 6, as shown in FIG. 3. In FIG. 2, theembossing pattern 23 is not shown for purposes of simplifying thedrawing. Then, the thus embossed cleaning sheet member 6 is fixed to thecase sheet member 4 by spotwise welding 12 and also by linear welding13, as already described before.

Polyvinyl chloride sheet that makes the cartridge case 1 (case sheetmember 4) softens at about 65° to about 85° C. and is plasticized atabout 120° to about 150° C. and starts to melt at about 170° C., asalready described, while the rayon fibers in the cartridge case-facingnon-woven fabric layer 16 decompose at about 260° to about 300° C. byheating without softening or melting. Thus, when the cleaning sheet 3(cleaning sheet member 6) is subjected to welding to the cartridge case1 (case sheet member 4) under some pressure, the rayon fibers 24 in thecartridge case-facing non-woven fabric layer 16 in the cleaning sheet 3(cleaning sheet member 6) are embedded into the inside surface layer ofthe cartridge case 1 (case sheet member 4), while retaining the fiberform, as shown in FIG. 11. Since the cross-sectional shapes of the rayonfibers 24 are non-circular, the cleaning sheet 3 can be firmly fixed toand held in the cartridge case 1, when the rayon fibers are embeddedinto the cartridge case 1 (case sheet member 4).

The remaining parts of the embedded rayon fibers 24 are in an entangledstate with one another and with the other fibers, or are heat sealed toone another, and ultimately the cleaning sheet 3 can be firmly fixed toand held in the cartridge case 1 thereby.

In this embodiment, the mixing ratio of the rayon fibers to thepolyethylene terephthalate fibers of 3:7 by weight in the cartridgecase-facing non-woven fabric layer 16 is used, but the mixing ratio canbe increased, for example to about 7:3 by weight.

FIG. 12 is an enlarged cross-sectional view of the cleaning sheet 3according to a fourth embodiment of the present invention, where thedisk-facing non-woven fabric layer 15 is composed of a thick singlelayer made of acrylic fibers alone, differently from the thirdembodiment, and the intermediate layer 17 is composed of a mixed fabricof acrylic fibers and rayon fibers. In FIG. 12, the intermediate layer17 is depicted as a layer of uniform thickness, but actually has no sucha uniform layer as depicted in FIG. 12 owing to the welding of theintermediate layer 17. Other structural members are substantially thesame as those of the third embodiment, and their description is omitted.

In this fourth embodiment, an embossing pattern can be formed on thesurface of the cleaning sheet member 6 as shown in FIG. 5 by knurlingtools to give the cleaning sheet member 6 a smooth sliding contact and agood cleanability to the magnetic disk. The present cleaning sheetmember 6 can be given the function and effect similar to those of theembossing by injecting a water jet to the cleaning sheet, when prepared,to form a large number of fine perforations beside the embossingprocessing.

As shown in FIGS. 9 and 12, the softness, cleanability, etc. peculiar tothe acrylic fibers can be fully obtained by making the thickness of thedisk-facing non-woven fabric layer 15 made of acrylic fibers only atleast twice the thickness of the cartridge case-facing non-woven fabriclayer 16 and that of the intermediate layer 17. According to a fourthembodiment of the present invention, a magnetic disk cartridge as shownin FIG. 1 is prepared by fixing a cleaning sheet composed of a fabric ofa single layer or a plurality of layers made of acrylic fibers alone tothe inside surface of a cartridge case by welding, where the shape, etc.of the cartridge case and the cleaning sheet are the same as those ofthe third embodiment, and thus their description is omitted.

Magnetic disk cartridge was prepared, using a cartridge case to whichthe cleaning sheet of said third embodiment was fixed by heat sealing(Example 3).

Cuttability, cleanability, magnetic disk scratchability, lintcharacteristics and weldability of the cleaning sheets of Example 3 weremeasured in the same manner as described before and are shown in Table 2together with those of Comparative Example, and Conventional Examples 1and 2 as given, referring to Table 1.

                                      TABLE 2                                     __________________________________________________________________________                            Scratch-                                                                             Lint                                           Sample Cuttability                                                                           Cleanability                                                                           ability                                                                              Characteristics                                                                       Weldability                            __________________________________________________________________________           No substantial                                                                        Much attachment Slight falling                                 Example 3                                                                            fluffy  of iron  No scratches                                                                         away of fibers                                                                        100                                                                              g                                          development                                                                           powders  observed                                                                             observed                                              No substantial                                                                        Much attachment No substantial                                 Comparative                                                                          fluffy  of iron  No scratches                                                                         falling away                                                                          10 g                                   Example                                                                              development                                                                           powders  observed                                                                             of fibers                                             No substantial                                                                        Rather less                                                                            Considerable                                                                         A few falling                                  Conventional                                                                         fluffy  attachment of                                                                          scratches                                                                            away of fibers                                                                        100                                                                              g                                   Example 1                                                                            development                                                                           iron powders                                                                           observed                                                                             observed                                              Many fluffy                                                                           Less attachment Slight falling                                 Conventional                                                                         development                                                                           of iron  Scratches                                                                            away of fibers                                                                        20 g                                   Example 2                                                                            observed                                                                              powders  observable                                                                           observed                                       __________________________________________________________________________

As is obvious from the foregoing test results, the present magnetic diskcartridge according to Example 3 has better cuttability, cleanability,magnetic disk scratchability, lint characteristics and weldability thanthose according to Comparative Example and Conventional Examples 1 and2.

According to the second aspect of the present invention, a highlyintegrated cleaning sheet without peeling off of the disk-facingnon-woven fabric layer and the case-facing non-woven fabric layer can beprepared by the presence of an intermediate layer composed of a mixedfabric of acrylic fibers and rayon fibers, and thus the presentinvention can also provide a magnetic disk cartridge having a cleaningsheet remarkably improved disk-handling characteristics and cartridgecase-fixing characteristics.

What is claimed is:
 1. A disk cartridge which comprises a cartridgecase, a disk rotatably encased in the cartridge case, and a cleaningsheet supported on the inside surface of the cartridge case by welding,the cartridge case being composed of a thermoplastic synthetic resin,and the cleaning sheet being composed at least of a mixed fabriccomprising acrylic fibers and rayon fibers and being fixed to the insidesurface of the cartridge case by welding.
 2. A disk cartridge accordingto claim 1, wherein the cleaning sheet is composed of a mixed fabric of80 to 20% by weight of acrylic fibers and 20 to 80% by weight of rayonfibers.
 3. A disk cartridge according to claim 1, wherein the cleaningsheet is composed of a mixed fabric comprising acrylic fibers, rayonfibers and heat-meltable fibers.
 4. A disk cartridge according to claim4, wherein the mixed fabric is composed of 80 to 20% by weight ofacrylic fibers, 15 to 60% by weight of rayon fibers, and 5 to 20% byweight of heat-meltable fibers, total being 100% by weight.
 5. A diskcartridge which comprises a cartridge case, a disk rotatably encased inthe cartridge case, and a cleaning sheet supported on the inside surfaceof the cartridge case by welding, the cartridge case being composed of athermoplastic synthetic resin, and the cleaning sheet being composed ofa sheet member of multilayer structure comprising a disk-facingnon-woven fabric layer composed of a non-woven fabric made mainly ofacrylic fibers on the disk-facing side, a cartridge case-facingnon-woven fabric layer composed of a non-woven fabric made mainly ofrayon fibers at least a portion of which are embedded into the insidesurface of the cartridge case by welding of the cleaning sheet to thecartridge case while substantially retaining the fiber form, and anintermediate layer linking the disk-facing non-woven fabric layer to thecartridge case-facing non-woven fabric layer, the intermediate layerbeing composed of a mixed fabric comprising acrylic fiber and rayonfibers.
 6. A disk cartridge according to claim 5, wherein thedisk-facing non-woven fabric layer is composed of acrylic fibers alone.7. A disk cartridge according to claim 5, wherein the cartridge case iscomposed of polyvinyl chloride and the cartridge case-facing, non-wovenfabric layer contains rayon fibers.
 8. A disk cartridge according toclaim 5, wherein the intermediate layer is composed of non-woven fabriccontaining thermoplastic fibers.
 9. A disk cartridge according to claim8, wherein the disk-facing non-woven fabric layer is a non-woven fabriclayer composed of acrylic fibers alone, the intermediate layer is amixed fabric layer composed of acrylic fibers and rayon fibers, and thecartridge case-facing non-woven fabric layer is a fabric layer composedof rayon fibers alone.